Thermal electric switch



Oct. 16, 1962 J. c. MATCHETT THERMAL. ELECTRIC SWITCH Filed Oct. 28, 1960 2 X, w y w Nv NQ om wm States ate 3,059,079 THERMAL ELECTRIC SWITCH John C. Matchett, Lakewood, Calif., assignor to Robertshaw-Fulton Controls Company, Richmond, Va., a corporation of Delaware Filed Oct. 28, 1960, Ser. No. 65,667 4 Claims. (Cl. 200-137) This invention relates to a thermal electric switch for controlling an electrical circuit and more particularly to a thermal electric switch responsive to and operable at ambient conditions of extreme high temperature and turbulent fluid flow.

In the past, thermal electric switches have been limited in their application by the lowest maximum temperature which any one component element of the switch can withstand before being deformed to thereby render the switch inoperative. Generally, these switches have a maximum operating temperature in the range of 800lo to 1000 F. If these prior devices are exposed for even a very short period of time to temperatures in excess of this range, the switch is likely to become either (l) unreliable at its previously accurate temperature or (2) inoperative.

The present invention utilizes the differential expansion of two dissimilar materials, which materials are capable of withstanding temperatures up to 2000i F. without affecting the operation or performance of the thermal electric switch.

lt -is an object of this invention to render a thermal electric switch completely reliable through a range extending frorn ambient temperatures to extremely high temperatures in the order of 2000" F.

Another object of this invention is a thermal electric switch operable in a high temperature, high speed turbulent atmosphere.

Still another object of this invention is to incorporate in a high temperature thermal electric switch adjustment means for varying the actuation of the thermal electric switch through a wide range of temperatures.

A further object of this invention is to construct a thermal electric switch from relatively inexpensive and durable materials capable of withstanding high temperatures.

These and other objects and advantages of this invention will become readily apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic view of an electrical circuit operatively connected to the thermal electric switch of this invention;

FIG. 2 is an enlarged partial longitudinal sectional view of the thermal electric switch of FIG. l;

FIG. 3 is an enlarged partial longitudinal sectional view of an embodiment of this invention; and

FIG. 4 is a cross sectional view taken on the line IV-IV of FIG. 2.

Referring now to the drawings, the thermal electric switch of this invention is contained in an elongated tubular housing which is formed from a heat resistant material, such as stainless steel, having a determinable coefficient of expansion. An adaptor plug 12, which has a threaded outer periphery, is secured to the housing 101, preferably by a shrink tit. Adaptor plug 12 mounts housing 10 in a suitable internally threaded aperture located in a wall 14 in a manner such that the temperature sensing end 16 of the switch extends inwardly of a heat source, such as a combustion chamber or heat baffle defined in part by wall 14.

A stationary contact pin 18 extends outwardly and substantially coaxial with the tubular housing 10. As will hereinafter be described, wall 14 forms a grounded connection 20 for the electrical circuit of the thermal electric switch. Stationary contact 18 is electrically connected to a suitable source of electrical energy 22 to form an electrical circuit which is as follows: Contact pin 18, thermal electric switch, housing 10, grounded wall 14, ground connection Ztl. Energization or deenergization of the thermal electric switch is determined by the thermal expansion of temperature sensing end 16 of housing 10.

Referring now to FIG. 2 a preferred embodiment is shown in which the housing 10 has a plurality of inwardly depressed tangs 24 formed adjacent a remote end 26 of housing 10. A spacer plug 28 is positioned substantially perpendicular to the longitudinal axis of housing l0 in abutting relationship with the inwardly depressed tangs 24. An elongated rod 30, formed from a material having a relatively low coeiiicient of expansion, such as quartz, is located within the housing 10 in such a manner that one end abuts against the spacer plug 28.

A substantially cylindrical movable contact 32 is positioned in abutting relation with the opposite end of rod 30 and is formed in such a manner that the outer peripheral surface 34 of contact 32 slidably engages the inner circular walls 36 of housing lil. A plurality of -axially extending curved prongs 38 are formed integrally on the central portion of the cylindrical body of the movable contact 32 and extend substantially coaxial with the longitudinal length of the housing 1b. Preferably, rod 30 is of a suiiicient length such that the end portion abutting against the movable contact 32 is located within the internal contines of adaptor plug 12.

It is apparent that as movable contact 32 is positioned within housing 10- adjacent to the comb-ustion chamber, movable contact 32 is preferably formed from a high heat resistant material, such as stainless steel, to thereby assure movement of the movable contact 32 within the contines of housing 10. In addition, the projecting prongs 38 of movable contact 32 are formed to accept and resiliently engage the inwardly extending portion 40` of the stationary contact 18. The prongs 38 formed on the movable contact 32 allow diametrical tension to be placed on the extended portion 40 of the stationary contact 18.

An internally threaded cap member 42 is secured to the end of the housing 10 projecting outwardly from the cornbustion chamber, as shown in FIGS. 2. and 3, and is thermally and electrically insulated from the tubular member 10 by a porcelain bushing 44 forming a sheath for the cap member 42. Stationary contact 18 is threaded intermediate its ends and thereby secured to cap member 42 to extend inwardly of housing 10 a sufficient distance to engage prongs 38 of movable contact 32. A slotted lock nut 48 secures the stationary contact 18 to the cap member 42 after the stationary contact 18 has been positioned within housing lil a desired distance.

A hollow sleevey member 50, which has an integrally formed peripheral shoulder 52 formed at one end, is positioned within housing 10 with the end surface 54 of shoulder 52 engaging the innermost radial surface of the cap member 42. Sleeve 50 is formed from a ceramic material which thermally and electrically insulates the movable contact 32 and stationary contact 18 from the housing 10. A compression spring 56 is positioned to extend between the shoulder portion 58 of movable Contact 32 and the shoulder 52 of the ceramic sleeve 50 to bias these members apart. The spring 56, therefore, biases the ceramic sleeve 50 into `engagement with cap member 42 and also biases the movable contact 32 into engagement with rod 30 and the .rod 30 into engagement with spacer plug 28. y

In operation, an increase in heat in housing 1() will cause longitudinal expansion and since the coeicient of expansion of the housing is greater than the coetiicient of expansion of rod at a predetermined temperature in the combustion chamber, the prongs 33 of movable contact 32 will disengage from the inwardly extenchng portion of stationary contact 10. Thus, the electrical circuit Will be opened whereby an appropriate alarm or indicator (not shown) will register this condition at the predetermined temperature.

The thermal electric switch described above can be readily adjusted to open a circuit at any predetermined temperature by simply varying the inwardly extending length of the stationary contact ltd and securing the stationary contact in place by means of the lock nut 53.

In FIG. 3, a normally open thermal electric switch unit is shown wherein identical structural elements are identitied by similar reference numerals as given in FIG. 2. The FIG. 3 embodiment is directed to a normally open thermal electric switch wherein a band of ceramic material 60 is formed on the stationary contact 1 3 adjacent its inwardly extending end 40. Upon the application of heat to the outer surface of housing 10, the housing will expand in length, thereby allowing the prongs of movable contact 32 to slide off the ceramic band o0 and into engagement with the outer portion d0 of stationary contact 18 to thereby close the electrical circuit.

It is to be understood that although several embodiments and modifications of this invention have been shown and described for purposes of illustration, the invention can be variously embodied and changes can be made in the construction and arrangement of parts without departing from the scope of the invention as defined by the appended claims.

I claim:

1. A thermal electric switch comprising a heat sensitive housing adapted for movement substantially in one direction when exposed to a source of heat, a heat insensitive means disposed within said housing for movement in response to movement of one wall of said housing, a movable contact spaced adjacent said heat insensitive means, a stationary contact oppositely disposed from said one wall for cooperable engagement with said movable contact, an insulated sleeve member encompassing said stationary contact, and means extending between said movable contact and said sleeve member for biasing said heat insensitive means into engagement with said one wall of said housing whereby thermal movement of said heat sensitive housing moves said movable contact relative to said stationary contact to energize an electrical circuit at a predetermined temperature.

2. A thermal electric switch comprising a heat sensitive tubular housing having one end wall, a heat insensitive member disposed within said housing and engageable with said one end wall, said heat insensitive member extending substantially the length of said housing, a cylindrical movable contact slidably engageable with the inner circular surface of said housing in operative engagement with the CFI free end of said heat insensitive member, a stationary contact positioned substantially coaxially within said housing for cooperable engagement with said movable contact, an insulated sleeve member formed-with a shoulder and having a length greater than said stationary contact positioned coaxially with said .stationary contact, and spring means subtending said sleeve member and extending between said shoulder and said movable contact for biasing said movable contact and said heat insensitive member into engagement with said one end wall of said housing whereby changes in temperature of said housing vary the length of said housing to move said movable contact relative to said stationary contact.

3. A thermal electric switch comprising a heat sensitive tubular housing having one end wall, a heat insensitive member disposed within said housing and engageable with said one end wall for axial movement therewith, said heat insensitive member extending substantially the length of said housing, a cylindrical movable contact slidably engageable with the inner circular surface of said housing, a stationary contact pin positioned substantially coaxially within sai-d housing, a plurality of curved prongs extending axially of said movable contact for cooperation with said stationary contact pin, said movable contact having a shoulder formed adjacent the peripheral edge thereof, an insulated sleeve member formed with a radial shoulder at one end positioned coaxially with said stationary contact, and helical spring means encompassing said sleeve member and extending between said shoulder of said sleeve member and said shoulder' `of said movable contact to thereby bias said movable contact and said heat insensitive member into engagement with said one end wall of said housing whereby changes in temperature of said housing vary the length of said housing to move said movable contact relative to said stationary contact.

4. The thermal electric switch dened in claim 3 wherein an electrically insulated ring is positioned intermediate the length of said stationary contact, said curved prongs of said movable contact normally engaging said ring whereby changes in temperature of said housing vary the length of said housing to move said prongs of said movable contact into engagement with the remote end of said stationary contact.

References Cited in the file of this patent UNITED STATES PATENTS 1,000,661 Beers et al Aug. l5, 1911 1,169,099 Wilcox et al Ian. 18, 1916 2,719,198 Cunningham Sept. 27, 1955 2,856,489 Bletz Oct. 14, 1958 FOREIGN PATENTS 411,465 Germany Mar. 28, 1925 323,905 Italy June l2, 1935 1,167,825 France Aug. 18, 1958 

